The invention relates to electro-optic modulators.
It is known in the art to employ Mach-Zehnder interferometers as electro-optic modulators in optical high-speed transmission systems, wherein, for example, coplanar travelling wave electrodes (TWE) are used to induce a phase shift in the interferometer arms. These TWEs comprise a first and a second coplanar microwave line connected to a plurality of periodically arranged and capacitively coupled electrodes on top of the waveguides. Examples of such TWE-Mach-Zehnder modulators are described in the publication “High-Speed III-V Semiconductor Intensity Modulators”, Robert G. Walker, IEEE Journal of Quantum Electronics Vol. 27, No. 3, March 1991. However, the electro-optic bandwidth of such TWE-Mach-Zehnder modulators is limited, for example, because of a mismatch between the electrical and the optical velocity, electrical losses in the device and impedance mismatching. Reducing the length of the electrodes may increase the bandwidth, wherein, however, a higher modulation voltage would then be required.
Another design concept of a Mach-Zehnder modulator is described in the publication “10 Gb/s-80-km operation of full C-band InP MZ modulator with linear-accelerator-type tiny in-line centipede electrode structure directly driven by logic IC of 90-nm CMOS process”, T. Kato et al., Optical Fiber Communication Conference and Exposition, 2011, p. 1, disclosing a Mach-Zehnder modulator comprising a plurality of separated waveguide electrodes arranged on the optical waveguides of the modulator, wherein multiple drivers are used to individually drive the waveguide electrodes (distributed driver or segmented electrode design).